Certain animal getting awfully rude (7)
I believe the answer is:
assured
'certain' is the definition.
(I've seen this in another clue)
'animal getting awfully rude' is the wordplay.
'animal' becomes 'ass' (term for a donkey).
'getting' means one lot of letters go next to another.
'awfully' is an anagram indicator.
'rude' with letters rearranged gives 'ured'.
'ass'+'ured'='ASSURED'
(Other definitions for assured that I've seen before include "Promised, guaranteed" , "without doubt" , "Confident - certain" , "Beyond doubt" , "Confident and self-possessed" .)